Press and drive mechanism therefor

ABSTRACT

The disclosure is directed to a long stroke extrusion press provided with an improved mechanical drive arrangement. The drive arrangement includes a linkage having a first drive link pivotally connected between the press slide and a second link which is connected to a driven crank. A third link is pivotally connected between the press frame and the second link. The various links are arranged to provide desirable kinematic and dynamic characteristics by developing a selected coupler curve at the pivot point between the first and second links.

United States Patent [1 1 Spachner et al.

PRESS AND DRIVE MECHANISM THEREFOR [73] Assignee: Gulf & WesternIndustrial Products Company, Grand Rapids, Mich. [22] Filed: June 24,1970 [21] Appl. N0.: 49,495

Related 0.8. Application Data [63] Continuation-impart of Ser. No.790,800, Jan. 13,

l 1969, abandoned.

[52] 1.1.5. Cl. 72/450, 100/282 [51] Int. Cl. B2lj 9/18 [58] Field ofSearch 72/452, 450, 451; 100/282 [56] References Cited UNITED STATESPATENTS 1,966,953 7/1934 Liebergeld 72/450 2,546,100 3/1951 Johansen72/450 2,696,165 12/1954 Hecht 100/282 2,781,015 2/1957 Dehn 72/4523,315,596 4/1967 Peters 100/282 FOREIGN PATENTS OR APPLICATIONS 410,3665/1934 Great Britain 100/282 OTHER PUBLICATIONSlndustrieblatt"Stuttqart, January l959-Germany (Article by Von DipL-ing.I-I. Rankers) Pages 1720.

Primary ExaminerCharles W. Lanham Assistant ExaminerGene P. CrosbyAttorney-Meyer, Tilberry and Body [57] ABSTRACT The disclosure isdirected to a long stroke extrusion press provided with an improvedmechanical drive arrangement. The drive arrangement includes a linkagehaving a first drive link pivotally connected between the press slideand a second link which is connected to a driven crank. A third link ispivotally connected between the press frame and the second link. Thevarious links are arranged to provide desirable kinematic and dynamiccharacteristics by developing a selected coupler curve at the pivotpoint between the first and second links.

24 Claims, 19 Drawing Figures PATENTEUumzs m:

SHEET 1 OF FIG. I

INVENTORS.

SHELDON A. SPACHNER 8 IEQAKASH D. DESAI z: and,

ATTORNEYS PAIENTEnucI 22 ms SHEET 2 OF 9 ATTQRNEYS sum 3 [If 9 'FIGQ3INVENTOR SHELDON A. SPAgZPERfi EEBAKASH 0. DE

ATTORNEYS PATENTEDBCI 23 I973 afresh-r1 SHEET l UF 9 2 aQWMAx.)

INVENTORS.

ATTORNEYS PRESS AND DRIVE MECHANISM THEREFOR This application is acontinuation-in-part application of our prior application Ser. No.790,800, now abandoned, filed Jan. 13, 1969.

The present invention is directed toward the press art and, moreparticularly, to an improved press and drive mechanism.

The invention is especially suited for use in high tonnage,comparatively long stroke extrusion presses and will be described withparticular reference thereto; however, it will be appreciated that theinvention is capable of broader applications and could be used in avariety of different types and sizes of presses.

Most present mechanically driven extrusion presses utilize aconventional slider-crank type of drive arrangement. The slider isdriven by a connecting link, or pitman, joined directly with the crankof the press. Due to inherent design limitations, this type of pressdrive results in a press which is uneconomical, especially in largersizes. Merely by way of example, assume that a standard designmechanical press is required to perform a work operation needing anapproximately constant force of 200 tons throughout a 6 inch workingstroke. Assume also, that a press is used which has a total stroke of 16inches and that the press develops its rated forces at one-half inchfrom the bottom of the stroke. It can be shown that a press of this typecan develop only 35 to 40 percent of its rated tonnage at a point 6inches above the bottom of its stroke when crank torque is at its ratedmaximum. Loading to greater values at this point will result inoverloading the crank, and overloading the gear reduction train. If aclutch is used in the drive train, the clutch will also be overloaded.And, if the press is directly driven (i.e., no flywheel or other energystoring device is used between the motor and reduction gear train), thepress motor will be overloaded as well. Consequently, to obtain therequired working force of 200 tons at the top of the 6 inch workingstroke, at least a 500 toncapacity press drive would have to be used.This would, of course, be extremely uneconomical since the press wouldbe capable of developing much more than the required 200 tons throughoutthe major portion of its stroke.

Not only would the press be uneconomical from the standpoint of itsdrive requirements, but also, it would require an unduly large frame.For example, the described press would be capable, at a point near thebottom of its stroke, of developing forces in the range approaching 400percent of its rated tonnage. In order to prevent inadvertent overloadsfrom destroying the frame, the rule of thumb is that the frame must becapable of withstanding three times the rated press tonnage.Consequently, in the subject example, the person wishing to have a presscapable of producing a 200 ton working stroke throughout a length of 6inches would be forced to use a press drive rated at 500 tons andequipped with a 1,500 ton capacity frame. The undesirable nature of thisis self-evident.

Many different types of drives and drive linkages have been proposed inattempts to overcome the noted disadvantages. The problem of providing adrive linkage which will overcome these disadvantages is especiallydifficult because in order to maximize press operational efficiency, thedrive linkage should preferably impart the following characteristics tothe press:

a. A minimum torque input requirement throughout a long working strokeso that the clutch and crank sizes required are minimized;

b. A relatively low slide velocity throughout the working portion of thestroke and a comparatively high slide velocity throughout all otherportions of the stroke so that high production rates can be obtained onmaterials having forming speed limits; and,

' c. A small transverse component of force applied to the slide toreduce side thrust on the slide and thereby reduce frame stress and wearon the gibs.

Point, or line contact mechanisms such as cams or rollers can developsuch characteristics in a press. However, such mechanisms cannot be usedfor highload applications because of the extremely high pressuresdeveloped at contact points.

In drawing presses there is another requirement which substantiallycomplicates efficient press design. Most metals must be drawn below aknown maximum velocity. For steel, the maximum velocity is approximatelyft/min. Assuming that the drawing stroke is 6 inches, the velocity ofthe slide must not exceed about 90 ft/min. over the last 6 inches ofslide travel. To perform this function in a standard slider-crank typepress, therotational speed of the crank must be reduced to a low level.Since one revolution of the crank corresponds to one cycle of the press,the production rate of the press is, by necessity, reduced. This haslong been the subject of press engineering attention, and many designshave been developed for reducing the velocity of the slide during onlythe drawing stroke. Hydraulically operated presses, cam driven pressesand drag link presses have been developed to provide a slow-downfunction in a drawing press. Also, it has been suggested to use twoseparate drive trains selectively operated by separate frictionclutches. Some of these prior presses included a crank directly abovethe slide so that the slide axis was through the pivot point of thecrank. This concept resulted in a drastic swing of the pitman and acorresponding increase in the side thrust on the slide. In additionthese concepts in press drive resulted in a toggle action at bottom deadcenter of the press which could generate high stresses on the crank pinand the crank journal structure at this slide position at nominal cranktorque. These various designs, when using only slider-crank linkages,did not de velop a coupler curve which results in optimum operation ofthe press slide. They also had limited ranges of slow-down capacities,were often subjected to undue torques and subjected the slide to highside thrusts.

The subject invention provides a press and drive linkage which meets allof the above-noted requirements, has no load limitations, andpermits'highly desirable kinematic and dynamic slide characteristics tobe obtained. This is accomplished by a unique combination of linkages, aunique output path created by this linkage and an advantageousrelationship of the output path to the path followed by the ram of thepress. By using this invention a wider variety of drawing press conceptscan be accomplished without substantial reduction of the totalproduction rate.

By use of the subject invention, substantial reduction may be made inthe size and strength requirements of the mechanical press drive andpress frame for execution of any operation requiring development ofvrated press force over a substantial portion of the stroke of the press.

In accordance with the invention there is provided a press whichincludes a frame and a slide member carried by the frame and mounted forreciprocal movement between first and second positions. Drive means areprovided for reciprocating the slide member between the first and secondpositions. The drive means includes a first link member having first andsecond end portions and having its first end portion pivotally connectedto the slide member. A crank member is rotatably mounted in the frameand a connecting link member has opposite end portions pivotallyconnected to the crank and the second end portion of the first linkmember. A constraining link member has one end portion pivotallyconnected to the frame and another end portion pivotally connected tothe connecting link member intermediate the end portions of theconnecting link member.

By varying the relative lengths of the link members, the press can havea large number of highly desirable characteristics generally defined bythe output curve of the upper pivot axis of the link connected to theslide. In fact, presses constructed in accordance with the invention canprovide characteristics previously economically obtainable only inhydrualic presses, if at all.

The above described invention is further defined by the output curvewhich it generates at the pivot axis between the first link (connectedto the slide) and the drive linkage associated therewith. This curvedefines the movement of the slide, or ram, as a function of time and itis generally called a coupler curve or coupler path.

In accordance with the present invention the lever system generates acoupler curve or path which allows the ram to move rapidly toward andaway from the bot tom dead center (BDC) of the ram except for theportion of the ram movement that accomplishes the drawing operation. Inthe work stroke the coupler curve or path creates a distinct slow-downin the velocity of the ram or slide. To perform this function, whichheretofore was generally performed by cams, clutches or hydraulicsystems, the coupler curve has a unique shape and disposition withrespect to the path of the slide driven thereby.

Accordingly, a primary object of the present invention is the provisionof a press and mechanical drive arrangement which permits highlydesirable kinematic and dynamic slide characteristics to be obtained.

Another object is the provision of a press having a mechanical drivearrangement which is especially suited for long stroke presses andcreates a slow-down of the slide in the drawing portion of the presscycle.

A further object of the invention is the provision of a mechanicallydriven press capable of producing relatively uniform slide forcesthroughout a comparatively long working stroke for a constantcrank'torque.

A further object is the provision of a press having relatively low crankinput torque requirement during the working stroke, permitting use of aclutch of relatively low torque rating.

A still further object is the provision ofa press which, when comparedto prior mechanically driven press, permits use of a lighter weightframe construction.

Yet another object is the provision of a mechanical press which iscapable of performing metal forming operations which in the pastrequired the use of hydraulically driven presses.

Another object is the provision of a lever system for driving a powerpress, which system generates a coupler curve disposed with respect tothe slide path in a manner to reduce side thrusts, reduce ram speed inthe work portion of the press stroke and increase the speed of the rambetween work portions of this stroke.

Still another object is the provision of a press of the general typedescribed which will considerably reduce the cost of deep-drawing andextrusion presses operating at current production rates.

An additional object is the provision of a mechanically driven presswhich permits a slow working stroke and rapid return stroke.

These and other objects and advantages will become apparent from thefollowing description when read in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a side elevation, having portions broken away, showing apreferred embodiment of a press formed in accordance with the presentinvention;

FIG. 2 is a front elevation of the press of FIG. 1;

FIG. 3 is a cross-sectional view taken on line 33 of FIG. 1;

FIG. 4 is a front view of the drive linkage used in the preferredembodiment;

FIGS. 5-8 are schematic diagrams showing the drive linkage at variouspoints in a complete cycle of the embodiment shown in FIGS. 1-4; I

FIG. 9 is an enlarged schematic view illustrating the linkage shown inthe prior figures and the coupler curve or path generated thereby;

FIG. 10 is an enlarged view illustrating the coupler curve or pathcreated by the linkage system of the previous figures;

FIG. 11 is a schematic view illustrating the lever system in a positionon the coupler curve wherein a maximum transmission angle occurs;

FIG. 11a is a schematic view illustrating another operatingcharacteristic of the present invention;

FIG. 12 is a schematic view showing the lever system on the couplercurve in a position wherein a minimum transmission angle occurs;

FIG. 12a is a schematic view illustrating another operatingcharacteristic of the present invention;

FIG. 13 is a chart illustrating certain operating characteristics of thepresent invention;

FIG. 14 is a chart illustrating other operating characteristics of thepresent invention;

FIG. 15 is a chart illustrating still further operating characteristicsof the present invention;

FIG. 16 is a schematic view illustrating another embodiment of thepresent invention;

FIG. 17 is a representative device used for the purpose of mathematicalanalysis.

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only, and notthe purpose of limiting the same, FIGS. 1 and 2 show the over-allarrangement of a long-stroke extrusion press formed in accordance withthe invention. The press shown is comprised of a vertically extendingmain frame assembly A, a drive unit B, and a mechanical drive linkageassembly C.

FRAME ASSEMBLY A Frame assembly A could be of a variety of constructionsand configurations; however, in the preferred embodiment it is shown asa vertical frame formed from weldment components. Specifically, theframe comprises a main base unit which houses and supports a verticallypositioned billet container 10a. Base unit 10 is mounted so its topsurface is flush with the floor l1 and two pairs of generallyrectangular box-like upright members 12 and 14 extend verticallytherefrom. The uprights l2 and 14 are joined at their upper ends by acrown assembly 16.

In the embodiment under consideration, the crown assembly 16 is athree-part structure formed from rectangular box sections 18, 20 and 22.The crown assembly 16 supports the drive linkage assembly C and isarranged so that the parting lines between the sections 18, 20 and 22coincide with the main pivot points of the drive linkage to facilitateconstruction and assembly.

The main structural components of the frame are joined by six verticallyextending tie rods. As shown, pairs of large diameter tie rods 24 passupward through each of the uprights 12. Single, smaller diameter tierods 26 pass upward through the front uprights 14. Referring to FIGS. 1and 3, it will be noted that the large diameter rods 24 are positionedan equal distance on opposite sides of the main drive linkage pivotpoints identified by reference letters D and 0. As will be apparenthereinafter, the tie rods 24 carry the main press reaction forces. Thesmaller diameter rods carry a minor portion of the reaction forces andfunction mainly to resist transverse slide reaction forces.

As is customary, the tie rods 24, 26 are preferably shrink fitted duringassembly of the frame. Additionally, the various mating surfaces betweenthe press frame components are keyed at several points (such as shown atlocation 28 in FIGS. 1 and 2) so as to lock the frame rigidly intransverse directions.

As can be seen from FIGS. 1 and 2, the uprights l2 and 14 are positionedso as to define the slideway or path of movement for the main pressslide or ram 114. Conventional gibs l2 and 14' are provided generally atthe inner corners of the uprights for guiding the slide through itsvertical path.

Although not shown, the press is equipped with the usual billet handlingand shear mechanisms, and the ad- DRIVE ASSEMBLY B Although the pressdrive assembly B could, of course, be mounted on the frame assembly A,in the preferred embodiment, it is carried on a separate support frameor stand 30 which is positioned adjacent the press. The main powersource for the press comprises an electric motor 32. As shown, motor 32is connected through a coupling 34 with a drive shaft 36 that supports alarge diameter flywheel 38. The flywheel 38 and shaft 36 are rotatablysupported in bearings or pillow blocks 40.

A conventional heavy duty, fluid actuated clutch 44 is mounted onflywheel 38 and, when actuated, functions to drivingly connect theflywheel with the main press drive shaft 42 through the shaft 46. Theshaft 46 is, as shown, suitably supported in pillow blocks 48 carried onframe 30.

As best shown in FIGS. 1 and 3, the drive train for the press is carriedin a two-part housing or gear box 52 which extends outwardly from theback of the press. The drive shaft 42 extends transversely through thegear box 52 and has a conventional brake 50 mounted at its outer end.Suitable bearings carried along the parting line of the housing 52support the drive shaft 42.

The drive train in the preferred embodiment is a gear train having aratio of 150 to 1. As shown, it includes a first main pinion gear 54keyed or otherwise positively connected to the drive shaft 42. Thepinion gear 54 drivingly engages a second gear 56 which is keyed to ahorizontally extending shaft 58 carried in conventional hearings in thedrive housing 52. A second pair of pinion gears 60 are also keyed toshaft 58 and positioned on each side of the gear 56. Gears 60 aredrivingly engaged with two relatively large diameter gears 62 which arekeyed to an elongated drive shaft 64 which extends transversely acrossthe back of the press and outwardly on both sides thereof. Two maindrive pinions 66 are positioned at the outer ends of shaft 64.

The drive pinions 66 each engage a separate, large diameter bull gear68. Referring to FIG. 3, it is seen that the bull gears 68 each includean annular gear section 70 which is welded to two spaced plates 72joined to a central hub 74. The central hub 74 is keyed or otherwisepositively connected to the outer ends of two stub shafts 76 carriedinthe crown of the press. Referring to FIG. 1, it is seen that the stubshafts 76 are mounted on the parting line between the crown sections 18and 20 and are provided with suitable sleeve bearings 78. As best shownin FIGS. 1 and 4, the inner ends of stub shafts 76 are keyed to two linkmembers 80 which carry a transversely extending wrist pin or shaft 82.This arrangement, in effect, forms a main drive crank having a throwequal to the distance between the center line 0 of stub shafts 76 andthe center line a of wrist pin 82.

DRIVE LINKAGE ASSEMBLY C Of particular importance to the presentinvention is the linkage arrangement provided to drivingly interconnectthe crank and the slide. As previously discussed, prior mechanicallinkage arrangements were generally unsatisfactory especially for use inlong stroke extrusion presses. For this reason, most of these presseswere hydraulically driven. The subject invention however, provides amechanical linkage arrangement which overcomes the problems of priormechanically driven presses. The arrangement provided permits highlydesirable dynamic and kinematic characteristics to be obtained.

Although a linkage assembly according to the invention could take avariety of specific forms, the preferred arrangement is as best shown inFIGS. 1 and'4. As shown there, the linkage assembly includes a firstlink member 84 which is pivotally'connected to the pin.

and its outer end is defined by a cylindrical portion 86.

The cylindrical portion 86 is provided with a slot 87 which receiveslink 84 and is connected thereto by a pair of pins 87a.

A pair of oscillating or constraining links 88'are pivotally mounted atone end to a horizontally extending shaft 92 which is carried in the topof the frame be-. tween the crown sections 20 and 22. It will be notedthat the center of shaft 92 (identified with a reference letter D) isvertically aligned with the center 0 of the stub shafts 76.Additionally, a vertical line passing through these two centers (i.e., 0andD) is parallel to the line or path of movement of slide 114.

The outer ends of the constraining links 88 are connected to thecylindrical end portion 86 of link 84 by split caps 90. As can be seenin FIG. 1, this provided a pivotal connection between links 88 and 84with an effective center of pivot at the center b of cylindrical portion86.

Extending transversely through the cylindrical portion 86 at a distanceL from its center is a relatively large diameter shaft or pivot pin 94.This pin extends outwardly on the opposite sides of the cylindricalportion 86 and is connected by caps 95 to the bifurcated upper end ofthe main slide drive link 98. The lower end of the drive link 98 is, ofcourse, pivotally connected to the slide assembly 104 which moves alonga slide axis F, as shown in FIGS. -9. As shown, this connection isprovided by a pin 100 which extends between a pair of bracket members102 which extend upwardly from a horizontal plate member 103 carried inthe slide assembly 104.

Although the slide assembly is generally conventional, its constructionshould be briefly noted. As shown, the previously mentioned member 103is adjustably connected to the slide 104 through a motor driven slideadjusting screw 106. This screw passes through a threaded opening in amember 108 received in the lower end of a sleeve 110 which forms aslideway or housing for member 103. Additionally, as can be seen, sleeve110 is closed at its lower end by a plate 112 which carries the main ramor slide assembly 114. The assembly 114 includes an outer housing 116which encloses main pressure blocks 118 and 120. The necessary extrusionram 122 and piercer 123 is releasably connected to the lower plate 124which is in turn positively connected to the housing 116.

Referring again more particularly to the drive linkage assembly C,attention is directed to FIGS. 5-8. These figures diagrammatically showthe link assembly as it passes through one complete cycle. The variouselements of these figures are identified with the same referencenumerals used to identify the corresponding elements in FIGS. l4however, because the elements are shown only diagrammatically, a primesuffix is added to avoid confusion.

FIG. 5 shows the linkage when the slide connection point E is at the topdead center. The crank is rotating in the clockwise direction and withthe particular linkage layout shown, the top dead center occurs when thecrank is at approximately 56rotation.

As the crank continues to rotatefrom the position shown in FIG. 5, theslide connection point E is driven down through an extrusion stroke andpasses through the position shown in FIG. 6. In the FIG. 6 showing, the

EXAMPLEI In the embodiment under consideration, the press is designed tohave a 131 inch total stroke and to be capable of a 36 inch workingstroke against a constant load resistance of 3,600 tons (extrusionstroke) and a 41.75

inch working stroke against a constant load resistance of 1,200 tons(piercing stroke). To accomplish this, the preferred lengths for thevarious linkageconnections are as follows:

0 to a distance equals 5 ft. 0 to b distance equals 7.5 ft. b to Cdistance equals 2.5 ft. b to D distance equals 10 ft. C to E distanceequals 15 ft. 0 to D distance equals 10 ft. 0 to F distance equals 8 ft.a to C distance equals 10 ft.

member (crank throw):

member 84' member 84' member 88 member 98' EXAMPLE II Fast approach andreturn slide velocity, and slow slide velocity through the workingstroke, can be achieved with the same, greater, or lesser, total strokeby variation of the above identified length relationships. As anexample, assume that it is desired to have a press capable of a 16 inchtotal stroke, and a 6 inch working stroke against a constant loadresistance of 200 tons. A satisfactory length relationship for theserequirements would be the following:

0 to a distance Member 80' (Crank throw) equals 9.44 in.

Member 84' a to b distance equals 16.53 in. Member 84' b to C distanceequals 7.27 in. Member 88 b to D distance equals 28.33 in. Member 98 Cto E distance equals 42.72 in. O to D distance equals 32.11 in. 0 to Fdistance equals 16.48 in. a to C distance equals 23.80 in.

The angle between a line from O to D and slide path F is 7, and thedistance 0 to F is measured at a right angle to this line between axes Oand D.

It is noted that, in this case, the general linkage arrangement is thesame, but the link ratios are not the same as those given in thepreferred embodiment. Nonetheless, this linkage will impart a fastadvance and fast return motion to the slide, and a slow motion throughthe 6 inch working stroke, in response to a constant angular velocity ofthe driving crank. Further, the maximum torque requirements would beapproximately 700 ton-inches.

OPERATION OF EXAMPLE ii To more fully describe the operation of thepresent invention, reference is made to FIG. 9 which is a schematicrepresentation of a drive system proportioned in accordance with EXAMPLEII. For the purposes of simplicity, various lengths and axes areidentified in accordance with the following legend:

First link link 98 Second link link 84 Third link link 88 Crank crank 80First axis axis E Second axis axis Third axis axis a Fourth axis axis CFifth axis axis D Sixth axis axis b Referring now to FIG. 9, as thecrank 80 rotates in accordance with arrow R, the fourth axis (C) movesalong the coupler curve which controls the movement of the first axisalong the slide path F. The shape of the coupler curve is so controlledthat the slide moves rapidly toward the working stroke, slowly throughthe working or'drawing stroke, and then rapidly to the top dead center(TDC). An analysis of the coupler curve is best shown in FIG. 10 whichillustrates the coupler curve intersected by the slide axis F to dividethe coupler curve into a first section" or sector, and a second section,or sector, with the first section generally corresponding to thelowermost position of the slide and a second section generallycorresponding to the upper portion of the slide movement. A major axisthrough the coupler curve is defined as the longest distance between twopoints in the curve. The minor axis is defined as the longest linebetween two points on the coupler curve and perpendicular to the majoraxis. The minor and major axes intersect at a point P. The relationshipof the first and second sections, the major and minor axes, and thevarious functional positions of the linkage arrangement will beexplained to fully appreciate the operating characteristics of thepresent invention. 7 t

The second section of the coupler curve includes the largest portion ofthe major axes. This section is on the side of slide path F opposite tothe crank 80. This second section relates to the faster motion of theslide and corresponds to the upper movement of the slide. By having thesecond section on the side ofpath F opposite from the crank, when thecrank is rotating toward the coupler curve a rapid velocity is created.This rapid velocity is enhanced by offsetting the crank on the other oropposite side of the path F. In this manner, the offset crank creates arapid motion when the axis C is in the second section. This rapid motionoccurs during both movement of the slide toward and away from the topdead center (TDC). The second section of the coupler curve has avertical height m and a horizontal length n. To provide a rapid upswingof the ram or slide, the height m is less than the length n. In a likemanner, the first section of the couplercurve has a height a and'a widthb. The height a is greater than the width b. Since the width b is acontributing factor to the side thrust of the slide during the power ofdrawing stroke, it should be maintained at a minimum. In practice, theratio of a to b' is generally above l.5:l.0. The ratio of m to n isgreater than 1.0 and preferably greater than about 1.5 11.0. Thisrelationship of the two section dimensions of the coupler curve providesthe rapid upswing and high power development in the downswing or workingstroke with a minimum of side thrust. The side thrust is generally inthe range of less than 10 percent of the total amount of load created onthe slide.

By offsetting the crank with respect to the path F, a more straight upand down movement can be created for the first link 98 during theworking or drawing portion of the stroke. If the crank were directly inline with the path F, a toggle action would be created whichnecessitates a wide swing of thelink 98 adjacent the bottom dead centerof movement. This creates substantial side thrust that can causesubstantial wear of the slide guides and requires extremely largesupporting structures. As can be seen in FIGS. 9 and 10, the major axisof the coupler curve intersects the slide path F at an obtuse angle k.This angle should be greater than about 110 and preferably greater thanabout 120 to assure that the coupler curve moves in a generally verticalinclined direction with respect to the path F.

Referring now to FIGS. l1, 12, 11a and 12a, other operatingcharacteristics of the present invention are schematically illustrated.The angle q shown in FIGS. 11 and 12 is called the transmission angle ofthe lever system. When this angle isapproximately 90 the most efficientforce ttransmission takes place. When this angle is relatively small,the most efficient motion transmission is effected. In accordance withthe invention, the transmission angle q, as shown in FIG. 11, is thegreatest when the ram or slide is moving toward the bottom dead center(BDC) position. This is when the best force transmission characteristicsis required. As .shownin FIG. 12, the angle q is the smallest when thefourth axis C is moving in the second section of the coupler curve. Thisis when the motion transmission is to be the most efficient in theillustrated embodiment. In accordance withthe preferred embodiment ofthe invention, the angle qshould not decrease substantially below 40 toavoid high slide acceleration, and rapid changes of slide acceleration.

In FIG. 11a, the coupler curve is illustrated as being divided intofirst and second sectionsby the slide path F, as previously described.In accordance with the preferred embodiment of the invention, when thecrank 80 overlies the second link 84, the fourth axis C is'well withinthe first section of the coupler curve. This causes the fourth axis-tomove slowly in a vertical direction as it .moves through the bottom deadcenter (BDC), shown on FIG. 1.1a. In other words, the overlying of thecrank and the second link-conditions the-fourth axis for a slow drawingoperation. Indeed, this'fourth axis is well within the first section ofthe coupler curve and is immediately ready to commence its downswingintothe bottom dead center position. This greatly enhances the forcetransmission and slow down characteristics of the linkage constructed inaccordance with the presentinvention. In FIG. 12a, anothercharacteristic of the-present invention is illustrated. In accordancewith this aspect of the invention, the crank 80 and'the third link 88have two positions. in which they are parallel. As-

- suming that the major axis of the coupler curve has terminal points PP, at the intersection withthe coupler curve, it is seen that when theparallel relationship exists between crank and third link 88 as shown insolid lines, the fourth axis C is moving downwardly along the couplercurve and is substantially spaced from both points P P In the otherparallel position, as shown in dashed lines, the axis C is substantiallyspaced from either point P P The fast motion of the linkage isdetermined primarily between these two parallel positions and over theupswing portion of the movment of axis C along the coupler curve. Thepoint P is just before the BDC position of the axis C as it moves alongthe coupler curve toward BDC.

When the power press is constructed with a linkage system which cancreate substantially one or all of the operating characteristicsillustrated in FIGS. 10, 11, 12, 11a and 12a, a highly efficient powerpress operation can be established in accordance with the objects ofthis invention. The combination of all of these features into one powerpress has been proven to be the most efficient utilization of thepresent invention.

Still further characteristics of the present invention should beexplained so that the total concept of the invention is readilyapparent. As previously explained, the crank 80 rotates about an axiswhich is offset from the slide path F. The link 88 swings about an upperaxis D in a downward arcuate path. The axis 0 of the crank is verticallybelow the pivot D of link 88 so that the link 88 is driven substantiallyalong a path corresponding generally to the coupler curve of the leversystem. By providing the crank connected on the end of link 84, link 84is pushed and pulled by rotation of the crank. This provides anefficient motion and force transmission operation which is modified bythe downward swinging characteristics of the link 88. This substantiallyreduces the force transmitting characteristics imposed upon the crankduring the operation of the linkage and assists in decreasing the torquerequirements of the crank. The major portion of the coupler curve, asdefined by the larger length of the major axis of one side or the otherof slide path F, is on the side of the slide path away from the crankaxis. It is also tilted upwardly and away from the crank axis and theslide member of the press. The axis b is closer to the axis 0 than it isto the axis a. In this manner, an efficient force transmission isaccomplished during the latter part of thedownward thrust acting upontheslide. All of these features define various aspects of the presentinvention which are unique in the press art and substantially enhancethe operating,characteristics of a press constructed in accordance withthe present invention.

Referrring now to FIG. 13, there is shown a chart illustrating acomparison between the operating characteristics of the presentinvention and the operating characteristics of a press constructed inaccordance with the prior art and-adapted for use in a drawingoperation. Assuming that the maximum drawing speed for steel isapproximately 90 ft/min, and the press is to have a 16 inch stroke witha drawing stroke of approximately 6 inches, during the last 6 inches ofthe power stroke, the velocity of the slide should not exceedapproximately 90 ft/min.

The solid line shows a press constructed in accordance with the presentinvention. The dashed line indicates a'press constructed in accordancewith the prior art. In the priorart, the crank speed is reduced to 21rpm so that velocity in the last 6 inches will not exceed approximately90 ft/min. It is noted that the up and down movement of the slidefollows generally along the same velocity curve. This is not true withthe present invention. The crank can be increased to rpm and still notexceed generally ft/min in the drawing stroke. As a press constructed inaccordance with the present invention has its slider, or ram, movingfrom bottom dead center (BDC) to top dead center (TDC), it circumscribesthe upper curve a having a maximum velocity of approximately 500 ft/min.On the down stroke, the velocity curve of a press constructed inaccordance with the present invention takes the form of curve b having afirst section I wherein the velocity increases to approximately 240ft/min and then decreases to approximately 90 ft/min at the 6 inchposition. Thereafter, curve b goes into a second section II wherein thevelocity generally fluctuates in the range of 90 ft/min. Thereafter, thevelocity curve for a press constructed in accordance with the presentinvention gradually decreases from approximately 90 to ft/min to zero inthe section of curve b labeled III. It can be readily seen by this curvethat a press can be operated substantially more rapidly whenincorporating the present invention. Since this curve does approachapproximately l00 ft/min in the drawing operation, it is anticipatedthat the speed of the press shall be reduced by approximately 10 percentto 54 rpm. Consequently, a press operated in accordance with the chartof FIG. 13 operates approximately 2.6 times faster than a pressconstructed in accordance with the present invention. This isapproximately 157 percent improvement in the production rate.

Referring now to FIG. 14, still a further characteristic of the presentinvention is illustrated. In this chart, the curve a represents apriorpress for creating a minimum tonnage of approximately 200 over thetotal working stroke of the 6 inch drawing operation. It is seen thatthe actual tonnage of such a press exceeds 1,700 tons at bottom deadcenter. If the prior press were reduced to a maximum tonnage ofapproximately 800 tons it would follow a tonnage curve b during thedrawing stroke. It is seen thata major portion of this curve issubstantially below 200 tons, the desired rating of this particularexample. When a press is constructed in accordance with the presentinvention, the tonnage curve follows curve 0. In this manner, it can beseen that a maximum tonnage of approximately 800 tons at bottom deadcenter is sufficient to provide approximately 200 tons over the completedrawing stroke of the press. These curves illustrate that; a pressconstructed in accordance with the present invention does not havetohave a frame which will withstand the tonnage requirements of the priorart when a minimum of 200 tons are to be exerted during the total 6 inchwork stroke.

Referring now to FIG. 15, another operating characteristic of thepresent invention is illustrated. This chart compares the torque of thecrank during the last'ap proximately 6 inches of the drawing. operationof a press constructed in accordance with the prior art as shown incurve a and a press constructed in accordance with the present inventionas shown in curve b. A peak torque of approximately 1,670 ton-inches isrequired .in a 200 ton-6 inch draw press so that'200 tons force can becreated'when the slide is approximately at the6 inch location. Inaccordance with the present invention, a

' press can be substantially reduced and the crank drive can be reducedin size and strength.

FIGS. 13-15 illustrate generalized operating characteristics of a pressconstructed in accordance with the present invention. Various otherpresses contructed in accordance with the present invention would varythese curves but not their general import.

EXAMPLE III Referring now to FIG. 16, another example of the presentinvention is illustrated. In accordance with this example, slide member200 is movable in a path F by the first link 202. A second link 204joins third link 206 with crank 208. A coupler curve is illustrated ascurve 210 having a major and minor axis, as illustrated. The numbersalong the coupler curve correspond with numbers along the arc of thecrank 208. The closer the corresponding points are located on thecoupler curve the slower the slide velocity, since the numbers on thecrank circle are equal increments of a uniformly rotated crank. As thespace increases between points on the coupler curve, the slide velocityis increased. First link 202 is connected between axis a and axis a.,.The second link is connected between axis a and axis a Stationary axis ais the center of the crank 208,.and stationary axis a is the centerofthe arc defined by the swinging third link 206. In accordance with thisexample, the following dimensions have been employed:

10.298 inches It is noted that the coupler curve illustrated in FIG. 16has the general characteristics of the coupler curve defined inaccordance with the Examples I and II. Also, the arrangement of thelinks although somewhat different in species is generically the same asthat described in connection with Examples I and II.'

Referring now to FIG. 17, a mathematical relationship drawing isillustrated to define points along a coupler curve 220 inrelation to twoorthogonal axes having their origin at the center of the crank. It isnot necessary to go into details of the various mathematicalrepresentations. The crank is r,, the second link is r the third link isr and the spacing between the two stationary axes O, C is r,. The fourthaxis is D which is coupled onto an appropriate first link, not shown. Bymathematical representations, the two equations for any point on thecoupler curve 220 areas follows:

2. Y,, r SIN 0, e SIN (0 (p) Referring again to FIGS. 5-8, it can beseen that the link on beam 84 remains in a state of bending during thestroke of the press. This is due to the spacing between axes b and c andthe fact that they are not vertically aligned with each other during thestroke. By this feature, the side thrusts of the slide are maintained ata low level.

The present invention has been described with certain embodiments;however, various other changes can be made to accomplish the structuredefined in the appended claims.

Having thus described our invention we claim:

1. In a power press comprising a frame; a slide member carried by saidframe for reciprocal movement along a generally straight slide pathbetween first and second positions; and a linkage drive means forreciprocating said slide member between said first and second positionswith a predetermined velocity-time relationship, the improvementcomprising: said linkage drive means including a first link memberhaving first and second end portions, with said first end portionpivotally connected to said slide at a first axis; a crank memberrotatably mounted on said frame at a second axis; a second link memberpivotally connected onto said crank at a third axis, spaced from saidsecond axis and pivotally connected to the second end portion of saidfirst link member at a fourth axis, and a third link member having oneend pivotally connected to said frame at a fifth axis and a second endpivotally connected to said second link at a sixth axis, said sixth axisbeing spaced from said third and fourth axes; said fourth axis definingan elongated generally elliptical coupler path when said crank member isrotated 360 about said central axis, said coupler path having a majoraxis defined by the longest line between any two points in said couplerpath and a minor axis defined by the longest line between two points insaid coupler path and perpendicular to said major axis, said major andminor axes intersecting at a point (P), said major axis having first andsecond ends, said first end of said major axis being closer to saidslide path than said second end and said point (P) being substantiallycloser to said first end of said major axis than to said second end ofsaid major axis.

2. In a power press comprising a frame; a slide member carried by saidframe for reciprocal movement along a generally straight slide pathbetween first and second positions; and a linkage drive means forreciprocating said slide member between said first and second positionswith a predetermined velocity-time relationship, the improvementcomprising: said linkage drive means including a first link memberhaving first and second end portions, with said first end portionpivotally connected to said slide at a firstaxis; a crank memberrotatably mounted on said frame at a second axis; a second link memberpivotally connected onto said crank at a third axis, spaced from saidsecond axis and pivotallyconnected to the second end portion of saidfirst link member at a fourth axis, and a third link member having oneend pivotally connected to said frame at a fifth axis and a second endpivotally connected to said second link at a sixthaxis, said sixth axisbeing spaced from said third and fourth axes; said fourth axis definingan elongated' generally elliptical coupler path when said crank memberis rotated 360 about said second axis, said coupler path having a majoraxis defined by the longest line between any two points in said couplerpath and a minor axis defined by the longest line between two points insaid coupler path and perpendicular to said-major axis, said major andminor axes intersecting at a point (P), said major axis having first andsecond ends, said first end of said major axis being closer to saidslide path than said second end and said point (P) being substantiallycloser tosaid first end of said major axis than to said second end ofsaid major axis and said velocity-time relationship, as said slidemember moves from said first to said second positions, includes a firstsegment wherein the slide velocity increases from zero to a maximumvelocity and then decreases to a preselected working velocitysubstantially less than said maximum velocity, a second segment whereinsaid velocity remains generally at said working velocity and a thirdsegment wherein said velocity decreases to zero, said first segmentbeing substantially greater than said second or third segments.

3. In a power press comprising a frame; a slide member carried by saidframe for reciprocal movement along a generally straight path betweenfirst and second positions; and a linkage drive means for reciprocatingsaid slide member between said first and second positions with apredetermined velocity-time relationship, the improvement comprising:said linkage drive means including a first link member having first andsecond end portions, with said first end portion pivotally connected tosaid slide at a first axis; a crank member rotatably mounted on saidframe at a second axis; a second link member pivotally connected ontosaid crank at a third axis, spaced from said second axis and pivotallyconnected to the second end portion of said first link member at afourth axis, and a third link member havine one end pivotally connectedto said frame at a fifth axis and a second end pivotally connected tosaid second link at a sixth axis, said sixth axis being spaced from saidthird and fourth axes; said fourth axis defining an elongated generallyelliptical coupler path when said crank member is rotated 360 about saidsecond axis, said coupler path defined by the formulae:

a. X r C080 e COS (0 w) b. =r SIN0 +eSlN(0 -l-m) wherein: X,, is a firstorthogonal component of the curve with an origin at said second axis; Ysecond orthogonal component of the curve with an origin at said secondaxis; r is the length of said crank; e is the fixed distance betweensaid third axis and said fourth axis; 0 is the variable angle of saidcrank with respect to said first component; 19 is the variable angle ofthe line between said third and sixth axes with respect to said firstcomponent; and w is the fixed angle between the line between said thirdand fourth axes and the line between said third and sixth axes; and,said coupler path having a major axis defined by the longest linebetween any two points in said coupler path and a minor axis defined bythe longest line between two points in said coupler path andperpendicular to said major axis, said major and minor axes intersectingat a point (P), said major axis having first and second ends, said firstend being closer to said slide than said second end and said point (P)being substantially closer to said first end of said major axis than tosaid second end of said major axis. 4. A method of driving thereciprocal ram of a power press along a slide path including a drivelink pivotally mounted on said ram and having a spaced pivot point, saidmethod comprising:

a. driving said spaced pivot point by a lever system and along anelongated, generally elliptical coupler curve; and,

b. modifying said elliptical curve to have a major axis defined by thelongest line between any two points in said coupler curve and a minoraxis defined by the longest line between two points in the coupler curveand perpendicular to said major axis, said major and minor axisintersecting at a point (P), said major axis having first and secondends, said first end being closer to said slide path than said secondend and said point (P) being substantially closer to said first end ofsaid major axis than to said second end of said major axis.

5. The improvement as defined in claim 1, wherein said second axis isoffset laterally in a first direction from said slide path, and saidfifth axis is offset from said slide path in said first direction.

6. In a power press comprising a frame; a slide member carried by saidframe for reciprocal movement along a generally straight slide pathbetween a lowermost and an uppermost position; and a linkage drive meansfor reciprocating said slide member between said first and secondpositions with a predetermined velocity-time relationship, theimprovement comprising: said linkage drive means including a first linkmember having first and second end portions, with said first end portionpivotally connected to said slide at a first axis; a crank memberrotatably mounted on said frame at a second axis; a second link memberpivotally connected onto said crank at a third axis, spaced from saidsecond axis and pivotally connected to the second end portion of saidfirst link member at a fourth axis, and a third link member having oneend pivotally connected to said frame at a fifth axis and a second endpivotally connected to said second link at a sixth axis, said sixth axisbeing spaced from said third and fourth axes; said fourth axis definingan elongated generally elliptical coupler path when said crank member isr0- tated 360 about said second axis, said coupler path having a firstend generally corresponding to move ment of said slide member in thevicinity of said lowermost position and a second end correspondinggenerally to movement of said slide member in said uppermost position,said coupler path having a major axis defined by the longest linebetween any two points in said coupler path, said major axis beinginclined with respect to said slide path and having a first end at saidfirst end of said coupler path, and said coupler path being positionedwith said first end thereof closer to said slide path than said secondend.

7. The improvement as defined in claim 6, wherein said slide pathintersects said coupler path between said first and second ends of saidcoupler path to divide said couplar path into corresponding first andsecond sections and intersects said major axis for the longer dimensionthereof to be in said second section of said coupler path. i g r 8. Inthe improvement defined in claim 7 wherein said transmission angle isthe largest when said ram is moving toward said lowermost position.

9. The improvement as defined in claim 1, wherein said fourth axis iscloser to said sixth axisthan to said third axis. j

10. The improvement as defined in claim 6, wherein said major axisintersects said slide path at an obtuse angle, said obtuse angle beingsubstantially greater than about 1 10.

11. The improvement as defined in claim 7, and a variabletransmissionangle between said second and third links, said transmission angle beingsmallest when said fourth axis is in the second section of said couplerpath.

12. The improvement as defined in claim 11 wherein said first sectionhas a third dimension parallel to said slide path and a fourth dimensionperpendicular to said slide path wherein said third dimension is greaterthan said fourth dimension.

13. The improvement as defined in claim 7, wherein said second sectionhas a first dimension parallel to said slide path and a second dimensionperpendicular to said slide path, and said first dimension issubstantially greater than said second dimension.

14. The improvement as defined in claim 7, wherein said first sectionhas a first dimension parallel to said slide path and a second dimensionperpendicular to said slide path, with the ratio of said first dimensionto said second dimension being at least 1.5 to l.

15. The improvement as defined in claim 7, and said fourth axis being insaid first section when said crank and second link overlie each other.

16. The improvement as defined in claim 7, wherein said first link formsa maximum angle with said slide path during movement of said slidetoward the extendedmost of said lowermost and uppermost positions, andsaid maximum angle being less than 30.

17. The improvement as defined in claim 7, and said fourth axis being ona line extending through said third and sixth axes.

18. The improvement as defined in claim 17 wherein said fourth axis isbetween said third and said sixth axes.

19. The improvement as defined in claim 1, wherein said coupler pathprovides for said crank member and second link member to overlie eachother when said slide member is moving toward the extended most of saidfirst and second positions.

20. The improvement as defined in claim 1, wherein said crank member andthird link member have two parallel positions and at least one of saidparallel positions occurs when said fourth axis is substantially spacedfrom both of said first and second ends of said major axis.

21. The improvement as defined in claim 20, wherein said one parallelposition occurs when said slide member is moving toward the extendedmost of said' first and second positions. 1

22. The improvement as defined in claim 6, wherein said coupler pathprovides for said crank member and second link member to overlie eachother when said slide member is moving toward said lowermost position.

23. The improvement as defined in claim 6, wherein said crank member andthird link member have two parallel positions and at least one of saidparallel positions occurs when said fourth axis is substantially spacedfrom both of said first and second ends of said coupler path.

I 24. The improvement as defined in claim 23, wherein said one parallelposition occurs when said slide member is moving toward said lowermostposition.

- Y 1TED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.- 766 f.- 771 Q 1 Datde [October 23, 1973 lnvencofls) Sheldon A. LSpa'chnerand Prakash D..Desai It is cerfi if ied that error appears in theabove-identified patent and that said Le'tfler Patent are herebycorrected as shown below:

Column 16 Qii ne 4 8 delete "7" and insert t l].

Signed e1 1 1'c 1 sealed this 27th day of August 1974.

(SEAL Attest:

MCCOY M. GIBSONQJR. c. MARSHALL DANN Attesting Officer, v Commissionerof Patents FORM Q v 1 r uscoMM-Dc 60376-P69 W U. S. GOVEINIINT'PIINTINGOFFICE llll O-Jl-SS,

1. In a power press comprising a frame; a slide member carried by saidframe for reciprocal movement along a generally straight slide pathbetween first and second positions; and a linkage drive means forreciprocating said slide member between said first and second positionswith a predetermined velocity-time relationship, the improvementcomprising: said linkage drive means including a first link memberhaving first and second end portions, with said first end portionpivotally connected to said slide at a first axis; a crank memberrotatably mounted on said frame at a second axis; a second link memberpivotally connected onto said crank at a third axis, spaced from saidsecond axis and pivotally connected to the second end portion of saidfirst link member at a fourth axis, and a third link member having oneend pivotally connected to said frame at a fifth axis and a second endpivotally connected to said second link at a sixth axis, said sixth axisbeing spaced from said third and fourth axes; said fourth axis definingan elongated generally elliptical coupler path when said crank member isrotated 360* about said central axis, said coupler path having a majoraxis defined by the longest line between any two points in said couplerpath and a minor axis defined by the longest line between two points insaid coupler path aNd perpendicular to said major axis, said major andminor axes intersecting at a point (P), said major axis having first andsecond ends, said first end of said major axis being closer to saidslide path than said second end and said point (P) being substantiallycloser to said first end of said major axis than to said second end ofsaid major axis.
 2. In a power press comprising a frame; a slide membercarried by said frame for reciprocal movement along a generally straightslide path between first and second positions; and a linkage drive meansfor reciprocating said slide member between said first and secondpositions with a predetermined velocity-time relationship, theimprovement comprising: said linkage drive means including a first linkmember having first and second end portions, with said first end portionpivotally connected to said slide at a first axis; a crank memberrotatably mounted on said frame at a second axis; a second link memberpivotally connected onto said crank at a third axis, spaced from saidsecond axis and pivotally connected to the second end portion of saidfirst link member at a fourth axis, and a third link member having oneend pivotally connected to said frame at a fifth axis and a second endpivotally connected to said second link at a sixth axis, said sixth axisbeing spaced from said third and fourth axes; said fourth axis definingan elongated generally elliptical coupler path when said crank member isrotated 360* about said second axis, said coupler path having a majoraxis defined by the longest line between any two points in said couplerpath and a minor axis defined by the longest line between two points insaid coupler path and perpendicular to said major axis, said major andminor axes intersecting at a point (P), said major axis having first andsecond ends, said first end of said major axis being closer to saidslide path than said second end and said point (P) being substantiallycloser to said first end of said major axis than to said second end ofsaid major axis and said velocity-time relationship, as said slidemember moves from said first to said second positions, includes a firstsegment wherein the slide velocity increases from zero to a maximumvelocity and then decreases to a preselected working velocitysubstantially less than said maximum velocity, a second segment whereinsaid velocity remains generally at said working velocity and a thirdsegment wherein said velocity decreases to zero, said first segmentbeing substantially greater than said second or third segments.
 3. In apower press comprising a frame; a slide member carried by said frame forreciprocal movement along a generally straight path between first andsecond positions; and a linkage drive means for reciprocating said slidemember between said first and second positions with a predeterminedvelocity-time relationship, the improvement comprising: said linkagedrive means including a first link member having first and second endportions, with said first end portion pivotally connected to said slideat a first axis; a crank member rotatably mounted on said frame at asecond axis; a second link member pivotally connected onto said crank ata third axis, spaced from said second axis and pivotally connected tothe second end portion of said first link member at a fourth axis, and athird link member havine one end pivotally connected to said frame at afifth axis and a second end pivotally connected to said second link at asixth axis, said sixth axis being spaced from said third and fourthaxes; said fourth axis defining an elongated generally ellipticalcoupler path when said crank member is rotated 360* about said secondaxis, said coupler path defined by the formulae: a. XD r1 COS theta 1 +e COS ( theta 2 + omega ) b. D r1 SIN theta 1 + e SIN ( theta 2 + omega) wherein: XD is a first orThogonal component of the curve with anorigin at said second axis; YD, second orthogonal component of the curvewith an origin at said second axis; r1 is the length of said crank; e isthe fixed distance between said third axis and said fourth axis; theta 1is the variable angle of said crank with respect to said firstcomponent; theta 2 is the variable angle of the line between said thirdand sixth axes with respect to said first component; and omega is thefixed angle between the line between said third and fourth axes and theline between said third and sixth axes; and, said coupler path having amajor axis defined by the longest line between any two points in saidcoupler path and a minor axis defined by the longest line between twopoints in said coupler path and perpendicular to said major axis, saidmajor and minor axes intersecting at a point (P), said major axis havingfirst and second ends, said first end being closer to said slide thansaid second end and said point (P) being substantially closer to saidfirst end of said major axis than to said second end of said major axis.4. A method of driving the reciprocal ram of a power press along a slidepath including a drive link pivotally mounted on said ram and having aspaced pivot point, said method comprising: a. driving said spaced pivotpoint by a lever system and along an elongated, generally ellipticalcoupler curve; and, b. modifying said elliptical curve to have a majoraxis defined by the longest line between any two points in said couplercurve and a minor axis defined by the longest line between two points inthe coupler curve and perpendicular to said major axis, said major andminor axis intersecting at a point (P), said major axis having first andsecond ends, said first end being closer to said slide path than saidsecond end and said point (P) being substantially closer to said firstend of said major axis than to said second end of said major axis. 5.The improvement as defined in claim 1, wherein said second axis isoffset laterally in a first direction from said slide path, and saidfifth axis is offset from said slide path in said first direction.
 6. Ina power press comprising a frame; a slide member carried by said framefor reciprocal movement along a generally straight slide path between alowermost and an uppermost position; and a linkage drive means forreciprocating said slide member between said first and second positionswith a predetermined velocity-time relationship, the improvementcomprising: said linkage drive means including a first link memberhaving first and second end portions, with said first end portionpivotally connected to said slide at a first axis; a crank memberrotatably mounted on said frame at a second axis; a second link memberpivotally connected onto said crank at a third axis, spaced from saidsecond axis and pivotally connected to the second end portion of saidfirst link member at a fourth axis, and a third link member having oneend pivotally connected to said frame at a fifth axis and a second endpivotally connected to said second link at a sixth axis, said sixth axisbeing spaced from said third and fourth axes; said fourth axis definingan elongated generally elliptical coupler path when said crank member isrotated 360* about said second axis, said coupler path having a firstend generally corresponding to movement of said slide member in thevicinity of said lowermost position and a second end correspondinggenerally to movement of said slide member in said uppermost position,said coupler path having a major axis defined by the longest linebetween any two points in said coupler path, said major axis beinginclined with respect to said slide path and having a first end at saidfirst end of said coupler path, and said coupler path being positionedwith said first end thereof closer to said slide path than said secondend.
 7. The improvement as defined in claim 6, wherein said slide Pathintersects said coupler path between said first and second ends of saidcoupler path to divide said couplar path into corresponding first andsecond sections and intersects said major axis for the longer dimensionthereof to be in said second section of said coupler path.
 8. In theimprovement defined in claim 7 wherein said transmission angle is thelargest when said ram is moving toward said lowermost position.
 9. Theimprovement as defined in claim 1, wherein said fourth axis is closer tosaid sixth axis than to said third axis.
 10. The improvement as definedin claim 6, wherein said major axis intersects said slide path at anobtuse angle, said obtuse angle being substantially greater than about110*.
 11. The improvement as defined in claim 7, and a variabletransmission angle between said second and third links, saidtransmission angle being smallest when said fourth axis is in the secondsection of said coupler path.
 12. The improvement as defined in claim 11wherein said first section has a third dimension parallel to said slidepath and a fourth dimension perpendicular to said slide path whereinsaid third dimension is greater than said fourth dimension.
 13. Theimprovement as defined in claim 7, wherein said second section has afirst dimension parallel to said slide path and a second dimensionperpendicular to said slide path, and said first dimension issubstantially greater than said second dimension.
 14. The improvement asdefined in claim 7, wherein said first section has a first dimensionparallel to said slide path and a second dimension perpendicular to saidslide path, with the ratio of said first dimension to said seconddimension being at least 1.5 to
 1. 15. The improvement as defined inclaim 7, and said fourth axis being in said first section when saidcrank and second link overlie each other.
 16. The improvement as definedin claim 7, wherein said first link forms a maximum angle with saidslide path during movement of said slide toward the extendedmost of saidlowermost and uppermost positions, and said maximum angle being lessthan 30*.
 17. The improvement as defined in claim 7, and said fourthaxis being on a line extending through said third and sixth axes. 18.The improvement as defined in claim 17 wherein said fourth axis isbetween said third and said sixth axes.
 19. The improvement as definedin claim 1, wherein said coupler path provides for said crank member andsecond link member to overlie each other when said slide member ismoving toward the extended most of said first and second positions. 20.The improvement as defined in claim 1, wherein said crank member andthird link member have two parallel positions and at least one of saidparallel positions occurs when said fourth axis is substantially spacedfrom both of said first and second ends of said major axis.
 21. Theimprovement as defined in claim 20, wherein said one parallel positionoccurs when said slide member is moving toward the extended most of saidfirst and second positions.
 22. The improvement as defined in claim 6,wherein said coupler path provides for said crank member and second linkmember to overlie each other when said slide member is moving towardsaid lowermost position.
 23. The improvement as defined in claim 6,wherein said crank member and third link member have two parallelpositions and at least one of said parallel positions occurs when saidfourth axis is substantially spaced from both of said first and secondends of said coupler path.
 24. The improvement as defined in claim 23,wherein said one parallel position occurs when said slide member ismoving toward said lowermost position.